In object detection, detection accuracy generally deteriorates when a covering object is present on a detection target. In image processing, such covering is also referred to as occlusion. As a technique for coping with occlusion, there is, for example, a technique described in PTL 1. The technique described in PTL 1 previously sets a hidden region, thereby reducing contribution of a feature value of the hidden region (e.g., see paragraph 0009, FIGS. 8 to 11).